<template>
  <div class="pagination">
    <!-- 起始部分 -->
    <button :disabled="pageNo === 1" @click="$emit('getPageNo',pageNo-1)">上一页</button>
    <button v-if="startNumAndEndNum.start > 1" @click="$emit('getPageNo',1)" :class="{active:pageNo == 1}">1</button>
    <button v-if="startNumAndEndNum.start > 2">···</button>

    <!-- 中间部分 -->
    <template v-for="(page,index) in startNumAndEndNum.end">
      <button :key="index" v-if="page >=startNumAndEndNum.start" @click="$emit('getPageNo',page)"
        :class="{active:pageNo == page}"
        >{{ page }}</button>
    </template>

    <!-- 结束部分 -->
    <button v-if="startNumAndEndNum.end < totalPage-1">···</button>
    <button v-if="startNumAndEndNum.end < totalPage" @click="$emit('getPageNo',totalPage)"  :class="{active:pageNo == totalPage}">{{ totalPage }}</button>
    <button :disabled="pageNo === totalPage" @click="$emit('getPageNo',pageNo+1)">下一页</button>

    <button style="margin-left: 30px">共 {{ total }} 条</button>
  </div>
</template>
<script>
export default {
  name: "PaginationIndex",
  // 1.接收数据
  props: ['pageNo', 'pageSize', 'total', 'continues'],
  computed: {
    // 2.计算一共有多少页
    totalPage() {
      return Math.ceil(this.total / this.pageSize)
    },
    // 计算出连续的页码的起始数字与结束数字【连续页码的数字：至少是5】
    startNumAndEndNum() {
      const { continues, pageNo, totalPage } = this
      // 先定义2个变了存储起始数字与结束数字
      let start = 0, end = 0
      // 如果总页数不够5页
      if (continues > totalPage) {
        start = 1
        end = totalPage
      } else {
        // 正常现象：连续页码5，但是你的总页数一定是大于5的
        start = pageNo - parseInt(continues / 2)
        end = pageNo + parseInt(continues / 2)
        // 把出现不正常的现象【start数字出现0|负数】纠正
        if (start < 1) {
          start = 1
          end = continues
        }
        // 把出现不正常的现象【end数字大于总页码】纠正
        if (end > totalPage) {
          end = totalPage
          start = totalPage - continues + 1
        }
      }
      return { start, end }
    }
  }
}
</script>

<style lang="less" scoped>
.pagination {
  button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
      color: #c0c4cc;
      cursor: not-allowed;
    }

    &.active {
      cursor: not-allowed;
      background-color: #409eff;
      color: #fff;
    }
  }
}
.active{
  background-color: skyblue;
}
</style>